1. Field of the Invention
This disclosure is related to the field of storage containers for contact lenses. More particularly, this disclosure relates to storage containers for contact lenses that are designed to indicate to a user when the contact lens container has reached the end-point of safe utilization and, therefore, must be replaced.
2. Description of Related Art
The contact lens is a corrective, cosmetic or therapeutic lens which is placed on the cornea of the human eye by a user. Soft hydrogel contact lenses have been available since the early 1970s, when the Czech chemist Otto Wichterle and his assistant Drahoslav Lim developed the first gel utilized in their production. Prior to the development of the soft hydrogel contact lens, the hard contact lens was the standard. This lens was made of rigid polymethyl methacrylate (“PMMA” or “Perspex/Plexiglas”). Some of the disadvantages of the hard PMMA lenses were: 1) that no oxygen was transmitted through the lens to the cornea, which could result in a number of adverse clinical effects; and 2) the long period of adaptation required before a comfort level for the user wearing the lens was achieved.
These problems of oxygen permeability and comfort are not associated with soft contact lenses, which are oxygen-permeable and are able to achieve immediate comfort for a user without a period of adaptation. Because of these inherent advantages, soft contact lenses quickly began to be prescribed to patients more often than hard contact lenses and became the predominant contact lens in the market—a position still held today.
The first generation of soft contact lenses were developed from polymer materials such as poly(hydroxyethyl methacrylate) (polyHEMA). These materials were highly flexible, hydrophilic or “water loving.” and compatible with the cornea and conjunctiva. However, despite their hydrophilicity, softness and flexibility, soft contact lenses still had the potential to have deleterious effects on the eye due to the possible interaction of microbes and toxic materials with the hydrophilic materials which comprised the lenses. Due to this risk, soft contact lenses were placed under the control of the Food and Drug Administration (FDA) when they were introduced into the United States in the early 1970s.
Since the first generation of soft contact lenses, there have been many developments in the field. These include the launch of the first silicone hydrogels in the late 1990s, second generation polymers that utilized the Tanaka monomer, and third generation polymers that utilized siloxy macromers. Each of the new generations of soft contact lenses offered improvements in oxygen permeability, wettability, comfort and clinical performance.
Despite improvements in soft contact lenses over the last twenty-five (25) years, there remain a number of issues that impede soft contact lenses from achieving widespread acceptance, the most paramount being the possibility of lens contamination with pathogenic microorganisms. Based in part on these issues, for the past ten (10) years the number of individuals wearing contact lenses has barely changed, being currently estimated at approximately two (2) percent of the worldwide population (about 125 million worldwide with an estimated 30 million of those located in the United States).
In order to keep the hydrogel materials which comprise a contact lens “soft” and in a hydrated state, they must be stored in a solution when they are not being used. Contact lens users typically have a case to store their current pair of contact lenses in solution when they are not being worn, such as when the user is sleeping. Solutions associated with contact lens care generally function as disinfectants, wetting agents and cleansers. In the early days of soft contact lenses, the storage solution for contact lenses was salt tablets dissolved in purified water to produce a 0.9% saline solution. However, without a disinfectant, this saline storage solution quickly supported bacterial growth, especially when misused. As a result, throughout the initial years of soft contact lenses, the lenses were typically heat disinfected in the saline storage solutions. While effective as a disinfectant, the heating process had numerous negative side effects, often resulting in the proteins from the tear film of the lens (which were absorbed into the lenses) being denatured (or deactivated). Often, these protein residues could not be removed from the lenses. In addition, heat disinfection was destructive to some variations of soft contact lens materials.
Due to the negative side effects associated with the heat disinfection method, it rapidly became apparent that some alternative process for disinfection was required. This led to the development of disinfection systems based on hydrogen peroxide, which were neutralized prior to reinsertion of the lenses onto the ocular surface by a prolonged saline soak. However, the hydrogen peroxide-based disinfection systems, while overcoming some of the negative side effects associated with heat disinfection, also had some major disadvantages associated with their utilization. These systems were complex, expensive and open to user misuse, with users frequently failing to remember to neutralize the lenses prior to insertion, resulting in significant ocular discomfort following reinsertion.
As a result of the negative side effects associated with both heat and hydrogen peroxide disinfection methods, preserved disinfection systems began to be developed in the mid-1970's. The most common preserved disinfection systems were based on chemical preservatives. These systems were initially based on mercurial compounds such as thimerosal or low molecular weight bisbiguanide antiseptics such as chlorhexidine. However, uptake of these mercurial compounds or low molecular weight bisbiguanide antiseptics into the hydrogel materials were high and their subsequent release onto the ocular surface resulted in high numbers of allergic complications for soft contact lens users. As a result, companies sought to develop higher molecular weight disinfectants that had lower uptake and release rates. Solutions which could meet the challenge of killing bacteria on stored lenses while not significantly concentrating in the material or otherwise producing a toxic lens were sought after. This resulted in the development of daily care disinfection regimens based on polyhexamethylene biguanide (PHMB) (e.g., Dymed® by Bausch & Lomb) or polyquatemary compounds such as polyquatemium-1 (e.g., Polyquad® by Alcon). More recently, these compounds have been supplemented with other biocides such as alexidine and myristamidopropyl dimethylamine (e.g., Aldox®).
No matter the solution or disinfection method used to store and clean contact lenses, for any user who utilizes contact lenses on a reusable basis, a suitable contact lens case is a necessary component of the contact lens cleansing and storage process. Accordingly, contact lens cases have existed in many forms since the initial stages of contact lens use and play a vital role in the storage, hydration and disinfection of contact lenses. For example, during the era of heat disinfection, contact lens cases needed to be able to withstand heat disinfection. Likewise, in the era of the hydrogen peroxide technique, the case sometimes contained a catalyst which facilitated the breakdown of the hydrogen peroxide. Currently, contact lens cases are often comprised of various plastics including, polyolefin, acrylonitrile butadiene styrene (ABS) and polypropylene designs.
Over the past twenty (20) years, it has become increasingly evident to those of ordinary skill in the contact lens field, that the contact lens case can be a major source for the microbial contamination of contact lenses, which can result in serious corneal infection. Even though many users realize the need to dispose of lenses after the recommended use period, many users do not realize that contact lens storage cases also have a limited period of safe and innocuous use. Even when a contact lens case is rinsed out and cleansed each morning after the lenses are removed and placed in a user's eyes, over time contaminants build up and the contact lens case becomes a fertile breeding ground for microbes. Notably, studies have shown that about 30-80% of the contact lens cases taken from asymptomatic lens wearers test positive for various pathogenic organisms including bacteria, fungi and Acanthamoeba. These pathogenic organisms attach to the contact lenses stored in the cases and, eventually, find their way onto the ocular surface following reinsertion of the lenses.
Generally, this is because the contact lens case often harbors a glycocalyx or “biofilm” that shelters microbes from the surrounding solution and prevents their adequate disinfection. Among symptomatic patients, up to one hundred percent (100%) end up with pathogenic colonies in their contact lens cases over time. Recent studies have demonstrated the difference in the effectiveness of currently utilized contact lens disinfection solutions to kill planktonic bacteria (i.e., those free in the environment) over sessile cells found primarily in the biofilm that are protected from disinfecting by the biofilm structure. Biofilms develop in contact lens cases from the absence of appropriate case cleaning, infrequent changing of solution, and/or structural breakdown of the case surface.
Accordingly, user compliance with proper contact lens and case disinfection and care is paramount to prevent the contamination of the lenses, storage container or both. While the introduction of multipurpose disinfection solutions has helped to alleviate some of the problems historically associated with inadequate cleaning of both lenses and cases, failure of a user to strictly comply with recommended disinfecting and cleansing techniques is still quite common. One of the reasons for this is that the contact lens cases currently utilized in the art are exclusively under the control of the user, who often cuts corners in contact lens care in order to save money or, simply, due to the careless aspects of human nature. Solution and case manufacturers and the optometrists and other professionals who prescribe the contact lenses and the proper disinfecting, care and cleansing regime have no control over case “misuse” by contact lens users. Misuse by users includes, but is not limited to, users keeping cases too long, reusing solutions designed for only one-time usage, topping-off old solution in the case with new solution, and inadequate cleaning and hygienic maintenance of the cases. All of these instances of misuse by users have been linked to microbial keratitis, one of the most significant complications of contact lens wear which has potentially devastating effects on the eye, including severe vision loss.
While attempts have been made to create contact lens cases that encourage compliant lens and case care regimens, these contact lens cases only employ passive control mechanisms that remind a user to empty the used solution, not to top-off, to adequately clean the case and to throw away the case at the end of its useable life. However, a user has often already been informed of the correct lens and case care regime by their eye care professional and still often chooses to ignore that advice. The problem in contact lens and case care is not a lack of information; rather, it is the human urge to obtain more usable life out of cases and solutions to cut costs or, simply, apathy towards proper lens care. By analogy, most humans know proper tooth care includes flossing once or more per day, but only about ten (10) to forty (40) percent of people floss every day. It is not a lack of knowledge; it is indolence. These problems will generally not be overcome by passive reminders. An active reminder that, beyond simply reminding, prevents a user from exceeding proper lens case use is needed.
Notably, none of these conventional contact lens cases currently provides such an active control mechanism, preventing a user from continuing to use a case after its safe and sterile lifetime and practicing the deleterious habits of reusing solution, topping-off old solution, and inadequate cleaning. While each of these practices might conserve a user's eye care expenses, each of these practices are counterproductive to safe, comfortable and proper lens care. These practices also expose a user to increased risk of eye infection and disease. Warnings of the potential deleterious effects of improper care and education on proper disinfection and cleansing methodologies are simply not enough to impede this practice of cutting corners that is all too common among contact lens users. Thus, there is a need in the art for an active control mechanism which simplifies contact lens care for a user, thus reducing the number of potential pitfalls and curbing the unhealthy and detrimental common “bad practices” associated with contact lens care, use and storage.